Sn—Ag—Cu solder alloys have been widely used as lead-free solders. The range of application of lead-free solder alloys is continuing to expand. As the use of the alloys has expanded, a desire has developed to use them in more severe environments. At the same time, a desire has also developed for high connection reliability such that a solder joint does not fracture or deteriorate even if used for long periods in such environments.
The environments of use of solder joints envisioned in this description are, for example, environments in which mobile phones, vehicle-mounted electronic parts, or the like are used. Evaluation of connection reliability is carried out by an accelerated test in a high temperature environment at a temperature of 125° C. or 150° C. for 500 hours or 1000 hours.
With the object of further improving conventional Sn—Ag—Cu solder alloys, it has been proposed to improve their connection reliability, resistance to drop impact, and wettability by adding Ni, Fe, or the like. Patent Documents 1-4 are representative examples of such proposals.
In recent years, because such solder alloys have been used for solder joints of printed circuit boards or packages for mobile phones or the like, there is a demand for a high degree of temperature cycle properties and connection reliability in high temperature environments. In order to cope with these demands, Patent Document 5 investigates a solder alloy containing P, Bi, or Sb in a Sn—Ag—Cu solder alloy. Patent Document 6 investigates a solder alloy containing Sb or Fe in a Sn—Ag—Cu solder alloy.